service = game:GetService("MarketplaceService")
extramoneyid = 20026140
extramoney = 100

service.ProcessReceipt = function(receipt)
    local players = game.Players:GetPlayers()
    for index=1, #players do
        local player = players[index]

        if player.userId == receipt.PlayerId then
            -- got the right player
            if receipt.ProductId == extramoneyid then
                -- they purchased the extra money product
                player.leaderstats.Cash.Value = player.leaderstats.Cash.Value + extramoney
                return Enum.ProductPurchaseDecision.PurchaseGranted
            end
        end
    end
end